Metal-containing or ash-forming detergents are widely used as additives in lubricating oil compositions (lubricants) for lubricating the crankcase of spark-ignited or compression-ignited internal combustion engines. Such additives may function to reduce or remove deposits and as acid neutralizers or rust inhibitors, thereby reducing wear and corrosion and extending engine life. They generally comprise a polar head with a long hydrophobic tail, the polar head comprising a metal salt of an acidic organic compound.
Conventionally, the acidic compound is derived from crude oil such as a sulfonic acid, a phenol or a salicylic acid.
This invention is concerned with detergents in which the acidic compound is derived from a natural product (such as oleic acid that is biocompatible and relatively low cost), and not from crude oil.
Surfactants are surface active agents. They are amphilic, meaning they contain two or more groups that are insoluble in each other. Structurally, they have a hydrophobic tail and a hydrophilic head.
Gemini surfactants (“Gemini” being a name assigned in 1991 to bis-surfactants) are sometimes called dimeric surfactants. They have more than one (usually two) hydrophilic head groups and more than one (usually two) hydrophobic groups in the molecule in contrast to conventional surfactants that generally have a single hydrophilic head group and a single hydrophobic group in the molecule.
The structure may or may not be symmetrical.
An example of a schematic representation of a Gemini surfactant is as follows:
TAILHEADSPACERHEADTAIL(hydrophobic)(hydrophilic;(hydrophilic;(hydrophobic)polar or ionic)polar or ionic)
The invention relates to use of gemini surfactant systems, i.e. dimers of monomeric surfactants linked with a spacer at the level of hydrophilic headgroups. The art contains many references to gemini surfactants. See, for example, J. Oleo. Sci. 60, (8) 411-417 (2011), “Oleic Acid-Based Gemini Surfactants with Carboxylic Acid Headgroups” by Kenichi Sakai et al. This reference describes their use only in aqueous systems and concludes that they may find application in the field of cosmetics, personal care, medicine, etc. No mention is made of non-aqueous application such as in lubricating oil compositions.